The thiopeptides, also referred to as pyridinyl polythiazolyl peptides, are a large family of peptide antibiotics that have undergone extensive posttranslational modification. Thiostrepton, like the other thiopeptides, has potent activity against Gram-positive bacteria, including those resistant to current antimicrobial treatments. The thiopeptides have also been reported to possess antimalarial and even anticancer properties. The process by which a fairly simple precursor peptide is converted to the highly complex molecular framework that characterizes this family of antibiotics is poorly understood. There are two main aspects to thiostrepton biosynthesis. The first is the tailoring of the peptide backbone that includes the dehydration of multiple serine and threonine side chains, the introduction of several thiazole rings, side chain oxidations, addition of an unusual quinaldic acid substituent, and the generation of two macrocyclic rings. The mechanism to introduce the dehydropiperidine ring of one of thiostrepton's macrocycles is the subject of much speculation. A separate aspect of thiostrepton biosynthesis is the generation of the quinaldic acid substituent from tryptophan. Our goals are: (1) To delineate the sequential steps required to produce this highly complex metabolite, (2) to characterize the unique enzymatic transformations of this pathway, and (3) investigate the utility of the thiostrepton biosynthetic machinery to generate new thiopeptides that can be evaluated for their antibacterial, antimalarial, and anticancer properties.